1. Field of the Invention
The present invention relates to an apparatus for serving a CAS broadcasting encrypted in various ways in a convergence system of broadcasting and communication.
2. Description of the Related Art
In order to effectively provide subscribers with a high speed/high capacity data service and a real time digital broadcasting/image service, data must be transmitted at a speed of more than 100 Mbps. However, such a high speed/high capacity data service and a real time digital broadcasting/image service cannot be provided by means of digital subscriber line (DSL) or a cable modem, which have attain at maximum a data transmission rate of merely 50 Mbps. In the spotlight at present, and as an outgrowth of research into types of high speed/high capacity data service, a passive optical network (hereinafter, referred to as PON) has been proposed as an economical solution.
PONs come in a number of varieties. There are, for example, ATM-PONs (Asynchronous Transfer Mode PONS), WDM-PONs (wavelength division multiplexing PONs) and Ethernet-PONs (hereinafter, referred to as EPON) which are based ATM-, WDM- and Ethernet-based, respectively. Moreover, for a high speed optical transmission to an ordinary home, a fiber to the home (FTTH) structure in the EPON has been proposed and is now being developed.
In general, the EPON has been basically developed to include communication data. In the EPON, for data transmission, an optical line terminal (hereinafter, referred to as OLT) transmits gigabit Ethernet signals at a speed of 1.25 Gbps to optical network terminals (hereinafter, referred to as ONTs) by means of a wavelength of 1550 nm. The ONTs likewise transmit gigabit Ethernet signals at a speed of 1.25 Gbps to the OLT, but by means of a wavelength of 1310 nm.
A growing need for broadcasting has required that the EPON employ broadcasting signals, and, for this, in an overlay broadcasting including method shown in FIG. 1, broadcasting signals are transmitted to the ONTs by means of wavelengths for broadcasting signals. These wavelengths differ from those utilized as communication data wavelengths.
FIG. 1 is a block diagram of a conventional EPON for convergence of broadcasting and communication.
As shown in FIG. 1, the conventional EPON for convergence of broadcasting and communication includes an OLT 100, multiple ONTs 200-1 to 200-N, a passive optical splitter 118, and an optical cable. The OLT 100 is a sub-system located between a user and a service node, receives a broadcasting signal and a communication signal from a broadcaster and a communication service provider, converts the signals into an optical signal containing bundled components corresponding to the electrical signals, and then transmits one tied optical signal. The multiple ONTs 200-1 to 200-N are user-side apparatuses and send information transmitted from the OLT 100 to a user. The optical cable connects the OLT 100 to the multiple ONTs 200-1 to 200-N.
Specifically, the OLT 100 performs a light conversion for a broadcasting signal transmitted through a broadcasting network through elements 115, 116, performs an optical amplification through element 117 for the converted signal, and then transmits the amplified signal. Further, the OLT 100 receives communication data from an internet protocol (hereinafter, referred to as IP) network through an IP router 111, converts the communication data into an optical signal through element 112, and then transmits the optical signal through element 113. The OLT 100 receives data from the ONTs 200-1 to 200-N and transmits the data to the IP network through the IP router 111.
Each of the ONTs 200-1 to 200-N receives a broadcasting signal through respective broadcasting receivers 119-1 to 119-N, and transmits the broadcasting signal to a user through respective broadcasting set-top boxes (STBs) 122-1 to 122-N. The ONTs 200-1 to 200-N also receive communication data through receivers 120-1 to 120-N, and transmit the communication data to a user through EPON ONT function processing units 123-1 to 123-N. Furthermore, the ONTs 200-1 to 200-N receive communication data transmitted from a user through the EPON ONT function processing units 123-1 to 123-N, and transmit the communication data to the OLT 100 through burst mode transmitters 121-1 to 121-N.
The above-described EPON for conventional broadcasting requires an erbium doped fiber amplifier (EDFA) 117, which is an expensive optical amplifier for amplifying a broadcasting signal, in order to enable an OLT 100 to transmit an analog broadcasting signal to the ONTs 200-1 to 200-N. On the other hand, if digital rather than analog broadcasting is involved, the expensive EDFA 117 is needed when the number of digital broadcasting channels increases.
Since all broadcasting channels are respectively transmitted to the ONTs 200-1 to 200-N, the ONTs 200-1 to 200-N need expensive optical receivers having specifications of high quality, such as high reception sensitivity and superior noise characteristic, in order to receive the transmitted broadcasting signals.
It is expected, moreover, that users will require in the future, in addition to digital broadcasting, real time digital image service of high quality. Unfortunately, however, the conventional EPON cannot deliver a real time digital image of high quality.
Furthermore, since the conventional EPON has no scheme (strategy; means; device) by which to enable the ONTs 200-1 to 200-N to transmit information regarding broadcasting to the OLT 100, it cannot realize an interactive broadcasting function which will eventually be required.